Variable resistor winding machine



March 1, 1955 J. R. MOORE 2,703,207

' VARIABLE RESISTOR WINDING MACHINE Filed April 24, 1946 5 Sheeis-Sheet 1 Ficgl.

Ihvez lTbOT: John R'Moore',

. HIS-AttOTI'18Y.

March 955 J. R. MOORE 2 ,2

VARIABLE RESISTOR WINDING MACHINE File d April 24, 1946 v s Sheets-Sheet 2 Inventor- John -R. Moohe,

H is Attorney.

J- R. MOORE VARIABLE RESISTOR WINDING MACHINE March 1, 1955 5 Sheets-Sheet 3 Filed April 24, 1946 04 01 I06 I I 3 Inventor: John Q. Moore,

His Attovney.

March 1, 1955 J. R. MOORE VARIABLE RESISTOR WINDING MACHINE 5 Sheets-Sheet 4 Filed April 24, 1946 m a] to 055 Inventor; JohnR. Moore,

Wi M His Attorney- March 1, 1955 J. R. M OORE VARIABLE RESISTOR WINDING MACHINE 5 /S heets-Sheet 5 Filed April 24, 1946 Inventor:

John F. Moore,

WWW His At't own ey.

United States Patent 2,703,207 VARIABLE RESISTOR WINDING MACHINE John R. Moore, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 24, 1946, Serial No. 664,471

23 Claims. (Cl. 242--9) This invention relates to apparatus for winding resistors, more particularly to apparatus for winding precision variable resistors, and it has for an object the provision of a simple reliable and efficient apparatus of this character.

More specifically the invention relates to apparatus for winding precision variable resistors having both linear and non-linear resistance characteristics whose percent variation of resistance is required to be in accordance with a desired mathematical function. In the past,

the Winding of precision resistors has required precision wire, very accurately constructed forms, very accurate measurement of the resistance after the winding was completed, and built-in means for varying the resistance at any one point to correct for winding errors. Consequently the production of precision resistors was slow and very expensive. Accordingly a further object of this invention is the provision of apparatus for producing such precision resistors rapidly from commercial materials thereby to result in low cost quantity production.

A more specific object of the invention is the provision of apparatus for winding precision resistors of which the percent accuracy and also the actual ohmic accuracy of the finished resistor can be held to Within the resistance of one turn of wire. 1

In carrying the invention into effect in one form thereof, means are provided for supporting an accuratewound master resistor, together with means for wind ing turns of wire on a supporting member. Means are also provided for continuously comparing the resistance of the turns from one end of the resistor being wound to the latest turn with the resistance of the turns occupying a corresponding space on the master. Any deviation of the ratio of these resistances from a predetermined value is utilized to produce a control voltage and.

means responsive to this control voltage are provided for varying the lead of winding turns on the supporting member to restore the ratio of the resistances to the desired predetermined value. In a specific embodiment of the invention the means for detecting deviations of the ratio of the two resistances from the predetermined value is a Wheatstone bridge having two ratio arms, a-third arm comprising the master potentiometer and a fourth arm comprising the turns wound on the supporting member. Means are provided for varying the number of turns of the master which are included in the. third arm as the winding of turns on the supporting member progresses. If the ratio of the resistance of the turns wound on the supporting member and the resistance of the turns of the corresponding portion of the master varies from the predetermined ratio, the bridge is unbalanced and a voltage appears across the output terminals. This voltage is amplified and used to control a motor to vary the lead of winding turns .on the supporting member to restore the predetermined ratio of the resistances.

For a better and more complete understanding of the invention reference should now be had to the following specification and to the accompanying drawings of which Fig. l is a simple diagrammatical sketch of an embodiment of the invention;

Fig. 2 is an exploded view in perspective of the winding mechanism;

Figs. 3 and 4 are details;

"ice

Fig. 5 is a simple schematic diagram of the electrical apparatus for controlling the winding operation;

Fig. 6 is a simple schematic diagram of the electronic control system for amplifying the output voltage of the bridge and controlling the speed and direction of rotation of the correcting motor, and Fig. 7 is a simple schematic diagram of the electronic apparatus known as the volume control for maintaining the voltage per turn of the master and the resistor being wound substantially constant.

Referring now to the drawings, a resistance wire 1, of ordinary commercial quality is to be wound upon a suitable supporting member 2 which is illustrated as a card. It is required that a predetermined ratio be maintained between the resistance of the Wire wound on the card measuredfrom one end to an arbitrarily selected point on the resistor and the resistance of a master resistor or potentiometer 3 measured from a corresponding end to a point which corresponds to the arbitrarily selected point of the resistor being wound. This ratio may be 1:1, but it is usually some other ratio.

The master is supported upon a suitable base member 4 to which it is clamped by suitable clamping means 5 One end of the card to be wound is firmly held by a clamp 6 and the other end is held by a clamp 7. The card is also supported in winding head 8 by means of a clamp 7a. This winding head has a drum 9 which is rotatably mounted in a supporting base member 10 by means of ball bearings 11 and 12. The drum 9 and the clamp 6 are driven synchronously from a splined shaft 13 to which they are connected through meshing gears 14 and 15 and meshing gears 16 and 17 respectively. An electric motor 18 drives the splined shaft through pinion gear 19 and driven gear 20.

The Winding head also carries the grooving mechanism and Wire guide in assembly 21. The grooving tool 22 projects an adjustable amount below a grooving guide 23 to provide for the cutting of grooves of different depths for different sizes of wire. The wire guides are a small steel ball bearing roller 24 with a small groove 24a cut in it and a rounded insulated block 24b. The

roller 24 is mounted on the grooving mechanism as close to the card being Wound as is consistent with safe clearance in order to insure laying the wire in the groove.

In addition-the winding head carries the stripping motor 25. This is a small high speed motor carrying a suitable abrading device such as the Wire Wheel 26. This may also be a grinding wheel for the purpose of grinding each wire fiat. The function of the abrading device is to remove insulation from the contact surface of the latest turn laid in the groove so that a contact 27 may make electrical contact with it for the purpose of resistance measurement.

Also the winding head carries a tension motor 28 on the shaft of which is mounted the spool 29 of wire from which the wire 1 is unwound and led through the winding guide to the card. A spring loaded slack arm 30 aids the tension motor in taking up slack.

As shown in Figs. 1, 2 and 4 the contact 27 is pivotally mounted on the sliding member 31a of a yoke 31 for limited rotation about an axis which is defined as the vertical axis of the aligned pivot pins 32 and 33. The yoke 31 is mounted on the drum 9 for rotation therewith. It is secured to the drum by suitable fastening means such as bolts (not shown). Compression springs 35 and 35a urge the sliding member 31a toward the unbroken straight edge 2a of the card, i. e. in the direction of the arrow 36.

The sliding member carries a roller 37 which acts as a follower in the cam groove 38 which is cut in the stationary cam member 39, which is secured to the support When the sliding member 31a moves forward, i. e.. in the direction of the arrow, a spring 40 rotates the contact member 27 in a counterclockwise direction againstthe stop formed by the rib 3112 thereby getting the contact out of the way of the grooving and stripping tools during that portion of the rotation in whiclrthese elements perform their functions. When the sliding member 31 moves in the reverse direction the lug 41a of't'he contact-carrying member 41 is first forced against the edge 2a of the card and the member 41 is then rotated in a clockwise direction against the, bias of spring 40. to elfect engagement of the contact 27 with the latest turn wound on the card thereby to provide for resistance measurement for a desired fraction of the revolution.

The wire 1 is connected to a binding post 42 before the first turn is wound. This binding post is connected to a slip ring 43 as shown in Fig. l and the contact 27 is con nected through conductors 44 and 45 to slip ring 46.

The winding head 8 is mounted on ball bearings which roll. on ways (not shown). It is driven by'lead screw 47- through split nut 48. As shown in Fig. 3, the split nut is spring loaded closed. It may be opened by the lever 49. to provide for manually traversing the head, for re moving or inserting a card, or setting up to wind.

The slip rings 43 and 46 provide for connecting the resistance wound on the card as one arm of a Wheatstone bridge of which the resistors 50 and 51 constitute the ratio'arms, and the resistor 2 being wound and the master resistor 3 constitute the third and fourth arms which are known as the balance arms, as shown in Figs. 5 and 7. The amount of the master resistor3 which is included in the fourth arm is determined by the position of the brush contact 52 which is carried in a brush assembly which in turn is mounted on a carriage 53. The carriage is mounted on ball bearings (not shown), which roll on ways (not shown) in the same manner as that described for the winding head. A lead screw 54 drives the carriage through a split nut 55 and a hand lever 56 serves to disengage the halves of the nut to provide for manual traversing to adjust the position of the master brush 52. The two lead screws are driven by the drive motor 18 through a mechanical differential device 57 of which one input element 57a is connected through gearing 58, 20, and 19 to the drive shaft of the motor 18 and the other input member 571) is connected through worm gearing 58a to the shaft of the correction motor 59. Connected to' correction motor 59 through gearing 144 there is a tachometer generator 145 for the generation of an electrical stabilization signal as will be described more fully below. The output member 57c of the differential is connected through gearing 60 to the lead screws 47 and 54. As shown in Fig. l the two lead screws aregeared together by means of gears 61 and 62. A friction clutch 54a is included in the connections.

As shown in Fig. 5, a direct voltage is supplied from a suitable power supply 63 to the input terminals 64 and 65 of the Wheatstone bridge. is in turn supplied from a suitable source of alternating voltage such as represented by the two supply buses 66 and 67 which are connected through a switch 68 and transformer 69 to a commercial A. C. source which is represented by the two conductors 70.

The structural details of the power supply 63 are illustrated within the dotted rectangle in Fig. 7. It comprises a bi-phase half wave rectifier valve 71 for rectifying the alternating voltage and a pair of control valves 72 and 73 of the high vacuum type energized from the rectified voltage for supplying a regulated direct voltage to the terminals 74 and 75 across which is connected a potentiometer 76. The magnitude of the voltage supplied to the bridge input terminals depends upon the position of the slider 76a on the potentiometer.

When the bridge is unbalanced, there appears across the output terminals 77 and 77a a direct voltage of which the magnitude depends upon the degree of unbalance of the bridge and the polarity depends upon whether, the rat o of the resistances of the third and fourth arms is greater or less than the ratio of the ratio arms 50.and 51. This direct voltage is amplified by means of a suitable electric valve amplifier 78. The amplified .voltage is utilized to energize the correction motor 59 for operatron m a direction to balance the bridge. As shown withm the dotted rectangle 78 in Fig. 6, the amplifier comprises a mechanical vibrator 79, a phase inverter amplifier, stage 80, a double ended push pull amplifierstage 81, a phase discriminator amplifier stage 82, and a thyratron power-amplifier, stage 83.

The" mechanical vibrator serves to.convert the direct signal voltage from the bridge to a square wave periodi- The D. C. power supply cally varying voltage. The square wave voltage is applied through a coupling capacitor 84 to the control grid of the first stage electric valve 85, which is supplied with direct voltage from a direct voltage power supply unit 86 which in turn is supplied from the alternating voltage supply buses 66 and 67. When a positive voltage is supplied to the grid of the valve 85 a resulting increase in current in the anode circuit produces an increased voltage drop across the anode circuit resistor 87 making the voltage at terminal 87:! less positive or more negative. Similarly, when a negative voltage is applied to the grid of valve 85. the resulting decreased anode current decreases the voltage drop across anode resistor 87 thereby making the voltage at the terminal 87a more positive. Thus the valve 85 operates as a phase inverter.

The terminal 87a is coupled by means of a capacitor 88 to the control grid of the valve 89 of the double ended push pull amplifier. The valve 89 together with valve 90 is supplied with direct voltage from the power unit 86. When a positive voltage is applied to the grid of valve 89 the increased anode circuit current produces an increased voltage drop across the anode circuit resistor thereby rendering the voltage of terminal 9111 less positive or more negative. The terminal 91a is coupled through the capacitor 92 to the grid of valve 90 and thus the negative voltage pulse at terminal 91a decreases the anode current of'valve 90-thereby decreasing the voltage drop across the anode circuit resistor 93 to make the terminal 93a more positive. Thus a positive voltage applied to the grid of valve 89 makes the terminal 9111 more negative and the voltage of terminal 930 more positive. A negative voltage applied to the grid of valve 89 produces voltages of the opposite polarities at these terminals. Alternating voltage is supplied from a suitable source to the anode circuits of valves 94 and 95; of the discriminator stage by. meansof transformers 96 and 97 of which the secondary windings are connected in the anode circuits of valves 94 and 95 respectively.

The capacitor 92 couples the terminal 91a to the grid of valve 94 and the terminal 93a is directly coupled to the grid of valve 95. Thus when a positive voltage is applied to the grid of valve 94 a negative voltage is applied to the grid of valve 95 and the valve 94 will conduct during the positive half cycles of anode voltage. Similarly, when a negative voltage is applied to the grid of valve 94, a positive voltage is applied to the grid of valve 95 and the latter valve will conduct during the positive half cycles of anode voltage.

Current flow in the anode circuit of valve 94 produces a voltage drop across resistor 98 which makes the voltage at the terminal 98a less positive or more negative. Since the valve 95 is non-conducting when valve 94 is conducting there is no voltage drop across resistor 99 and the voltage atterminal 99a becomes increasingly positive.

The terminals 98a and 99a are directly coupled to the grids of thyratrons 100 and 101. These thyratrons are supplied from a source of alternating voltage which is represented by the supply conductors 102. The circuit for thyratron 100 is traced from upper supply conductor 102 through upper contacts of time delay relay 103, conductor 104, upper contacts of contactor 105 (Figs. 5 and 7'), contacts of switch 106, armature of correction motor 59, forward split field winding 59a, conductor 107,'anode and cathode of thyratron 100 to ground and the opposite side of source 102. The circuit for thyratron 101 is similarly traced through the reverse split field winding 59b and conductor 108.

When valve 94 is non-conducting and terminal 981: is positive, thyratron 100 is conducting and the motor 59'rotates in the forward direction. Similarly, when the valve 95 is non-conductive, thyratron 101 is conducting and the motor 59'rotates in the reverse direction.

From the foregoing it is-seen that if the bridge is unbalanced so that the voltage of the terminal 77 is positivewith respect to-thevoltage of terminal 77a the correction motor will rotate in the forward direction, and similarly if the'voltage of terminal 77 is negative with respect to the voltage of terminal 77a the correction motor rotates. in the reverse direction.

Whenever the correction motor 59 rotates, the tachometer.;generator 145,; describcd in connection with Fig. l, is also rotated to generate a velocity signal voltage proportional to the velocity of correction-motor 59. The armature of the tachometer generator is connected valves 94 and 95 are subjected to a shift in D. C.v

voltage potential due to the tachometer generator signal across resistor 147 to cause an early decrease in the output of the phase discriminator amplifier stage 82 to stabilize the system. This type of stabilization signal is often called an anticipation signal and is highly useful in preventing any overshoot and hunting or instability of the system.

A switch 109, Figs. 1, 5 and 7, is actuated by a cam 110 which is connected to the driven gear 17 to open and close its contacts once during each revolution of the card. The cam is initially adjusted so that it causes the switch to close contacts 109a and to open contacts 1091) and 1090 during the half revolution of the card in which contact 27 is in contact with the resistance wire 1 and to open contacts 109a and close contacts and 1090 during the remaining half revolution. Contacts 10% and 109c in closing ground the amplifier 78;

in the open position contacts 10% and 10% remove the ground and contact 109a in closing completes an energizing circuit for the operating coil 1110 of contactor.

111. In response to energization contactor 111 closes its normally open contacts 111b, lllc and 111d and opehs its normally closed contacts 111e, 1117', 111g and 1111.

Contacts lllb and 111c in closing complete the bridge circuit and also complete the connections from the bridge output terminals 77 and 77a to the amplifier 78.

With the foregoing understanding of the elements and their organization the operation of the machine will readily be understood from the following description.

The switches 106, 112, 1 13, 68, 114 and 115 are closed, and the brush motor and the tension motor 28 are energized. With the winding head in position to begin winding and the carriage in the correct initial; position the carriage limit switches 116a, 116b, 1160 and 116d are closed thereby to complete'an energizing circuit forthe operating coil 105c of contactor 105 which picks up and closes its contacts 105b and 105a to complete the connections of the drive motor 18 to the A. C. source to initiate the winding operation and simultaneously to complete the connections of rection motor 59 to the thyratrons. Q

As long as the ratio of the resistance of the wire wound on the card between the binding post 42 and the latest turn and the resistance of the turns occupying a corresponding space on the master is the same as the ratio of the ratio arm resistors 50 and 51, the bridge is balanced and no voltage appears across the output terminals. Consequently no signal voltage is transmitted to the amplifier and the correction motor remains at standstill. However, if owing to some non-uniformity in the resistance wire being wound or error in card construction, the resistance of the turns wound on the card is too great, relative to the resistance of the turns in the corresponding space on the master, the bridge becomes unbalanced and the voltage at the terminal 77 becomes positive with respect to the voltage of terminal 77a. As a-result, the motor 59 is energized for rotation in a direction such that the rotations of the input members 57a and 57b of the differential device are added and the speeds of the lead screws 47 and 54 are correspondingly increased thereby increasing the lead of winding turns on the card 2. This increase in the lead promptly rebalances the bridge and terminates the correcting action.

Similarly, if the resistance measured at the latest turn on the card is too low relative to the resistance of the master at the corresponding position the bridge is unbalanced in the opposite sense and thevoltage at the terminal 77 becomes negative with respect to the voltage at the terminal 77a. Consequently, a negative signal voltage is supplied to the amplifier and the correcting motor is energized for rotation in the reverse direction. The rotation of the input member 57b subtracts from the rotation of input member 57a and the'speeds of the lead screws are correspondingly decreased. This decreased speed of the lead screws reduces the lead with the cor- 6 which turns are wound on the card. The decreased lead promptly restores the correct ratio thereby rebalancing the bridge and terminating the correcting action.

Thus the resistance of the wire being wound is measured during the winding of each turn and any error, i. c. any deviation from the correct ratio with respect to the master is promptly detected and corrected. The result is that the resistor is wound so that its resistance from one end to any arbitrary point corresponds accurately to the resistance between an end and a corresponding point of the master.

In order that a predetermined unbalance voltage across the terminals 77 and 77a shall indicate the same amount of error at all positions on the card, it is necessary to compensate for differences in length of wire per turn. This is accomplished by varying the position of the slider 76a on the potentiometer 76 thereby to vary the voltage supplied to the bridge so that the voltage measured across a predetermined number of turns between the contact 52 and the contact 52a is maintained reasonably constant.

During the half revolution of the card in which the contacts 111 are closed, the voltage between contacts 52 and 52a is amplified by the amplifier 117 shown in Fig. 7. If this voltage exceeds a reference voltage across the resistor 119, the electric valve 118 in the output stage of the amplifier is rendered conducting thereby to complete an energizing circuit for the operating coil of contactor 120. In response to energization, contactor 120 picks up and closes its contacts 120a partially to complete the connection of the armature of the slider motor 121 to the source. During the half revolution of the card in which the resistance is being measured, the contacts 111d are closed to complete an energizing circuit for the operating coil of contactor 122 which picks up and opens its contacts 122a and 1221). At the end of this half revolution of the card, the contactor 122 is dropped out to close contacts 122a and 122b. In closing, contacts 122]; connect the anode and cathode of electric valve 123 across the primary of transformer 124. Since the grid voltage of this valve is more positive than the cathode voltage, the valve becomes conducting and energizes the operating coil 125a of contactor 125 which immediately responds to pick up and open its contact 1251). At the expiration of a very short time delay the capacitor 126 becomes charged by grid rectification current. The polarity of this charge is negative at the grid terminal and consequently the valve is rendered non-conducting. As a result, the contactor 125 drops out and closes contacts 125b to complete the armature circuit for the motor 121 through contacts 1200 to the D. C. source. This effects rotation of the motor in a direction to move the slider 76a downward to reduce the voltage supplied to the bridge. This compensating action is terminated when the voltage between the contacts 52 and 52a becomes equal to the reference voltage across resistor 119.

Similarly, if the voltage between contacts 52 and 52a becomes less than the reference voltage, the electric valve 127 is energized and the reverse contactor 128 is picked up to close its contacts 128a to effect rotation of the motor in the reverse direction. The slider 76a is moved upward to increase the voltage supplied to the bridge. This continues until the voltage between the contacts 52 and 52a is equalized with the reference voltage thereby terminating the compensating action. Overtravel of the slider in either direction is prevented by limit switches 76b and 760 in the motor circuit.

A safety cut-off is provided for deenergizing the lead correcting motor 59 in the event of an excessive error voltage resulting from a break in the wire being wound on the card, poor contact with the bare portion of the turn or other condition resulting in an excessive error signal. When the error signal voltage is within the normal range, the electric valves 129 and 130 are conducting. See Fig. 67 As a result of the current conduced by valve 130, contactor 131 picks up and opens its contacts 131a and 131b. The capacitor 132 is connected through a rectifier valve 133 to the grid of the valve 89 of the push pull amplifier stage and consequently it becomes charged in proportion to the error signal. If the error signal is excessive, the voltage across capacitor 132 makes the voltage of the grid of valve 134 sufliciently negative to render it non-conducting. The resulting decrease in the voltage drop across resistor 135 makes the grid voltage of valve 136. sutiiciently positive to render the valve conducting. The current conducted by valve 136 produces a voltage drop across resistor 137 which decreases the grid voltage of valve 130 thereby decreasing the energizing current of contactor 131 sufficiently to cause the contactor 131 to drop out and close its contacts 131a and 13112. This short-circuits the output circuit of the push pull amplifier stage and stops the correction motor. In the brief instant before the contacts are closed, the negative voltage applied to the grid of valve 130 is also applied to the grid of valve 129 and interrupts its conduction. As a result of the decreased voltage drop across resistor 138 the grid voltage of valve 139 becomes sufficiently positive to render the valve conducting to complete a short circuit across the output circuit of the push pull stage through valves 139 and 140. This short circuit is of brief duration because it is interrupted as soon as the charge on capacitor 141 is dissipated. However,

by this time the contactor 131 has closed the contacts 131a and 13111 to maintain the short circuit.

By varying the position of the slider 14111 on the potentiometer 141 the per cent of full speed of the correcting motor 59 in the reverse or lead reducing direc tion may be varied. If the slider is at the top of the potentiometer, which is connected to the negative side of the source, any positive signal voltage on the grid of the valve 94 will cause the valve 140 to become conducting, thereby connecting the grid of the valve 94 to the negative side of the source and preventing energization of the thyratrons to effect rotation of the motor in the reverse direction. If the slider is at the bottom of the potentiometer, the cathode of valve 140 is positive and consequently a positive voltage on the grid of valve 94 does not cause the valve 140 to become conducting. a result the positive voltage on the grid of valve 94 can effect rotation of the correcting motor at full speed in the reverse direction. For intermediate positions of the slider 141 the correcting motor operates at corresponding intermediate speeds.

Although in accordance with the provisions of the Patent Statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A potentiometer Winding machine comprising in combination means for supporting a master potentiometer,

means for winding turns of wire on a turn supporting member, and means responsive to a change in the ratio of the resistance of the turns wound on said supporting member and the resistance of the turns occupying a corresponding space on said master potentiometer for varying the lead of winding turns on said supporting member.

2. A potentiometer winding machine comprising in combination, means for supporting a master potentiometer, means for winding turns of wire on a turn support ing member, means for comparing the resistance of the turns wound on said member with the resistance of the turns occupying a corresponding space on said master potentiometer, and means responsive to a change in the ratio of said resistances for varying the lead of winding turns on said supporting member.

3. A potentiometer Winding machine comprising in combination, means for supporting a master potentiometer, means for Winding turns of wire on a turn supporting member, means for comparing the resistance of the turns wound on said member with the resistance of the turns occupying a corresponding space on said master potentiometer once during the winding of each turn, and means responsive to a change in the ratio of said resistances for varying the lead of winding turns on said supporting member.

4. A potentiometer winding machine comprising in combination, means, for supporting a master potentiometer, means for Winding turns of wire on a turn supporting member, means for comparing the resistance of the turns wound on said-member with the resistance of the 8 turns occupying a corresponding space on said master potentiometer during the interval of winding a predetermined portion of each turn, and electric motor means responsive to a change in the ratio of said resistances for varyingthe lead of winding turns to restore said ratio.

5. A potentiometer winding machine comprising in combination, means for supporting a master potentiometer, means for winding turns of wire on a turn supportingmember, a Wheatstone bridge having a pair of ratio arms, a third arm comprising said master potentiometer and a fourth arm comprising the turns wound on said supporting member, means for progressively varying the number of turns included in said third arm as the winding of turns on said member progresses, and means responsive to an unbalance of said bridge for varying the lead of winding to maintain a substantially constant ratio between theresistance of the turns wound on said supporting member and the resistance of the turns occupying a corresponding space on said master potentiometer.

6. A potentiometer winding machine comprising in combination, means for supporting a master potentiometer, means for winding turns of wire on a turn supporting member, a Wheatstone bridge having a pair of ratio arms, a thirdarm comprising said master potentiometer and a fourth arm comprising the turns wound on said supporting member, means for progressively varying the number of turns included in said third arm in correspondence with the instantaneous winding position on said supporting member, electric valve means responsive to a voltage across opposite points of said bridge for amplifying said voltage, and motor means controlled by said electric valve amplifying means for varying the lead of winding to maintain a substantially constant ratio between the resistance of the turns wound on said supportingmember and the resistance between one terminal of said master potentiometer and a point thereon corresponding in position with the position of the latest turn wound on said supporting member.

7. A potentiometer winding machine comprising in combination, means for supporting a master potentiometer, means for winding turns of wire on a turn supportingmember, a Wheatstone bridge having a pair of ratio arms, a third arm comprising said master potentiometer andafourtharm comprising the turns wound on said supporting member, means for progressively varying the number of turns included in said third arm in correspondencewith the instantaneous winding position on said supporting-member, electric valve means responsive to i a voltage across opposite points of said bridge for amplifying said voltage, motor means controlled by said electr-ic valve amplifying means for varying the lead of windingto maintain a substantially constant ratio between the resistance of the turns wound on said supporting member and the resistance between one terminal of said master potentiometer and a point thereon corresponding in position with the position of the latest turn wound on said supporting, member, and a tachometer generator driven by said motor means for supplying a voltage to the input circuit of said electric valve means to stabilize the correcting actionof said motor means.

8. A method of winding a precision resistor having a resistance characteristic accurately predetermined by that of a reference standard comprising, winding resistance wire on a card to form a resistor, continuously comparing the resistance value of said resistor during winding with that of a corresponding variable portion of the standard, and continuously modifying a unit dimension of said resistor in response to deviations in the resistance value thereof from that of said portion of the standard.

9. A method of winding a precision resistor having a resistance characteristic substantially identical to that of a reference standard comprising, winding resistance wire on a card and relatively transversely moving the feed wire and the card to form a resistor, continuously comparing the resistance value of said resistor during winding with that of a corresponding variable portion of the standard and continuously varying the speed of the transverse movement between the feed wire and the card to modify the-pitch of said resistor in response to deviations in the resistance value thereof from that of said portion of the standard.

10, Apparatus for winding a precision resistor having aresistance characteristic accurately predetermined by that ofarcference standard comprising, a winding mechanism including means for winding resistance wire on a resistance card and advancing means for producing relative transverse movement between said card and said feeding means to form a resistor, means for continuously comparing the resistance value of said resistor during winding with that of a corresponding variable portion of the standard, and means responsive to deviations in the resistance value of said resistor from that of said portion of said standard for varying the speed of said advancing means to vary the pitch of said resistor winding.

11. A potentiometer winder comprising in combination, a rotatable winding form support adapted to carry a winding form on which resistance wire is to be wound, movable lead screw means for feeding resistance wire to the winding form as it is being rotated, means for driving both the rotatable winding form support and the lead screw means with an adjustable speed ratio, a master potentiometer with resistance varying means driven by the lead screw means, and a resistance comparator responsive to the relationship between the resistance of wire wound upon the winding form and the master potentiometer resistance for varying said speed ratio adjustment to vary the pitch with which wire is wound on the winding form for correcting deviations between the resistance function of the wound wire and that determined by the master potentiometer.

12. A winding machine comprising, in combination, a rotatable winding form support adapted to carry a winding form upon which an electrical device is to be wound, movable lead screw means for feeding material to the winding form as it is being rotated, means for driving both the rotatable winding form support and the lead screw means with an adjustable speed ratio, a master variable element with means driven by the lead screw means for varying an electrical characteristic thereof, and an electrical comparator responsive to the relationship between magnitudes of predetermined electrical characteristics of the master element and the electrical device being wound for varying said speed ratio adjustment to vary the form of the electrical device being produced for correcting deviations between magnitudes of the characteristics of the device being wound and the master.

13. In a potentiometer Winder having a master potentiometer and a rotatable winding form driven simultaneously with means for making electrical connections to the master potentiometer and the portion of the wire wound on the wire form, a resistance comparator connected to said electrical connections, a winding pitch control motor and an amplifier interposed between said resistance comparator and said motor for varying the operation of the motor in response to deviation between resistances of the master potentiometer and the portion of the wire wound upon the winding form.

14. Apparatus for driving first and second shafts with an adjustable speed ratio comprising, in combination, a driving motor for the first shaft, an error correction motor, a differential having input shafts mechanically connected respectively to said driving motor and said error correction motor and having a differential output shaft connected to drive said second shaft, impedance means connected for varying at a predetermined rate dependent upon the rotation of the first shaft, additional impedance means dependent in magnitude upon relationship between the shaft speeds, and error signal means responsive to relationship between said impedances for driving said error correction motor.

15. In a potentiometer winder having a winding form rotator and a wire traverser, a differential for varying the speed relationship between the winding form rotator and the wire traverser, and means responsive to resistance error for overdriving the differential.

16. In a potentiometer winder having a winding form support, wire feeding means, mechanism for relatively rotating the winding form support with respect to the wire feeding means, and means for traversing one of said elements with respect to the other, a differential for varying the speed relationship between the rotating means and the traversing means, and means responsive to resistance error for overdriving the differential.

17. A resistance winding machine comprising driving means for turning a resistance support, means for feeding a wire to said support, a driving connection including speed varying means between said driving means and said feeding means for moving said feeding means at a me determined adjustable speed to feed the wire to said support in a predeterminedspacfed turn relation, a motor for operating said speed varying means, means for producing a pulsating voltage varying in phase and value with the difference between the resistance of the wire wound on the support and a desired resistance up to that point, means responsive to the phase and value of said voltage for energizing said motor for forward or reverse rotation for adjustment of said speed varying means to increase or decrease the speed of said wire feeding means for wire turn spacing adjustment, and means responsive to rotation of the support for limiting the operation of said motor to a predetermined period of time during each revolution of the support.

18. A method. of manufacturing precision electrical resistors having a precisely defined resistance characteristic which comprises the steps of continuously winding electrical resistance wire on a support, continuously comparing the resistance value of the wound portion of the resistor with a corresponding portion of a standard resistance having a desired calibration, and continuously adjusting the rate of winding the electrical resistance wire to follow the calibration of said standard resistance element.

19. A device for manufacturing precision electrical resistors which comprises a mandrel for winding a wire wound resistance element, a null indicating bridge arrangement, means to connect the resistance element as one arm of the bridge, a standard wire wound resistance element having a desired calibration, means to connect a portion of said standard resistance element having a resistance value corresponding to the wound portion of the resistance element being wound on the mandrel as a balancing arm of said bridge arrangement, a continuously movable contact on said resistor, a movable contact on said standard resistance element, means coupling said resistor contact and said standard resistance contact whereby said resistor contact follows said standard resistance contact and the resistance of said resistor can be calibrated to follow the calibration of the standard resistance, means to continuously rotate said mandrel to wind a resistance element, and means responsive to deviations from a null indication on said bridge for controlling the speed of winding said resistance element to thereby obtain a resistance element having a calibration comparable to the calibration of the standard resistance.

20. A potentiometer winding machine comprising in combination means for supporting a master potentiometer, means for winding turns of wire on a turn supporting member, means responsive to a-change in the ratio of the resistance of the turns wound on said supporting member and the resistance of the turns occupying a corresponding space on said master potentiometer for varying the lead of winding turns on said supporting member, and switch means operable in response to said winding means for periodically connecting and disconnecting said resistance ratio responsive means.

21. A potentiometer winding machine comprising in combination, means for supporting a master potentiometer, means for winding turns of wire on a turn supporting member, a Wheatstone bridge having a pair of ratio arms, a third arm comprising said master potentiometer and a fourth arm comprising the turns wound on said supporting member, means for progressively varying the number of turns included in said third arm as the winding of turns on said member progresses, means responsive to an unbalance of said bridge for varying the lead of winding to maintain a substantially constant ratio between the resistance of the turns wound on said supporting member and the resistance of the turns occupyint a corresponding space on said master potentiometer, and means operable during each cycle of operation of said winding means for disconnecting and reconnecting said lead varying means.

22. A potentiometer winding machine comprising in combination, means for supporting a master potentiometer, means for winding turns of wire on a turn supporting member, a Wheatstone bridge having a pair of ratio arms, a third arm comprising said master potentiometer and a fourth arm comprising the turns wound on said supporting member, means for progressively varying the number of turns included in said third arm' in correspondence with the instantaneous winding position on said supporting member, electric valve means responsive to a voltage across opposite points of said bridge for amplifying said voltage, motor means conat trolled. byv said electric valve' amplifying means for varying, the lead of winding to maintain a substantially constant ratio between the: resistance: of the. turns wound,

on said supporting member and the resistance between one terminal of. said: master potentiometer and a point thereon, corresponding; in position with the position of the latest turn wound on said supporting member, switch means operable duringthe. winding of each turn by said winding. means for disconnecting and reconnecting said electric. valve means, and atachometer generator driven by said motor means for supplying a voltage to the input circuit of said electric valve meansto stabilize the correcting action of said motor means.

23. A potentiometer winder comprising in combination,. a rotatable. winding form support adapted to carry a Winding form on which resistance wire is to be'wound, movable lead screw means for feeding resistance wire to the winding form as. it is being rotated, means for 12 driving: both: the rotatable winding form support and the lead'screw meanswithranadjustable speed ratio, a. master potentiometerwith resistance varying means driven by the lead:- screw means,- a resistancecomparator responsivev to the relationship between the resistance of wire wound upon the winding form and the master potentiometer resistance for varying said speed ratio adjustment to vary the pitchwith which wire is wound on the winding. form for correcting deviations between the resistance function of the Wound wireand that determined by the master potentiometen. and-means connected tosaid support and operable duringv each rotation thereof to momentarily disconnect, said' resistance comparator.

References Cited inthe file of this patent UNITED STATES PATENTS 2,500,605 DesLange et a1. Mar. 14, 1950 

